Physical Quantities

• Ruler (rule)


  Used to measure the length of an object between 1mm and 1m
• Measuring the volume of an object of irregular shape


  1. Place it into a measuring cylinder full of water

  2. The water level rises

  3. The rise is equal to the volume of the object
• Micrometer screw gauge


  Used to measure very small distances that a rule cannot measure
• Analogue and digital clocks and devices


  Used to measure time intervals
• Finding an average value for a small distance and for a short time interval


  Measure multiples (including the period of a pendulum)
• Mass

  A measure of how much matter is in an object
• Weight

  A gravitational force (the effect of a gravitational field on a mass) measured in Newtons
• Weights (and hence masses) can be compared using a balance
• Same object on two different planets


  The mass is the same, but the gravitational field strength (g) on the two planets will be different (i.e. not 9.8N/kg for both) so the weight is different
• Acceleration in free fall is due to gravity, and is the same as g, i.e. 9.8m/s²
• Density

  The mass per unit volume: density = mass / volume
• To find the density of a liquid


  Find the mass of the measuring cylinder by placing it on a balance, then fill it with the liquid and measure the new mass. The difference in masses is the mass of the liquid. The volume can be read from the cylinder and the density calculated using the equation.
• To find the density of a solid


  Measure the mass of the solid by placing it on a balance. If the solid is regularly shaped, measure its dimensions using a ruler or other measuring tool and then use a mathematical formula to find the volume. If the solid is irregularly shaped, immerse it in water and measure the volume of the water displaced. This is the volume of the solid. Find the density using the equation.
• The density of water is 1g/cm³
• If the density of an object is greater than 1g/cm³

  It will sink in water
• If the density of an object is less than 1g/cm³

  It will float in water
• The gravitational field strength on Earth is 9.8N/kg
• Force = Mass × Acceleration (F=ma)
• Weight = Mass × Gravitational Field Strength (W=mg)